Negative pressure underfire control system

ABSTRACT

A control system responsive to the draft flow of air within a burner for regulating the supply of combustion air to the burner interior. A plate is disposed within a draft opening of the burner with linkage connecting the plate and the underfire air system of the burner. The linkage is operable to translate plate motion into movement of components associated with the underfire system to increase or decrease underfire air in relation to internal burner temperatures as the draft flow of air is proportional to burner temperatures.

United States Patent 1191 111 3,848,551 Cramer Nov. 19, 1974 1 NEGATIVE PRESSURE UNDERFIRE 7 3,730,114 5/1973 Stone et al. .1 110/18 R CONTROL SYSTEM 3,731,640 5/1973 Stutz 110/18 R [76] lnventor: William H. Cramer, 1510 College 4 St. Apt. D-4, Lacey, Wash. 98503 [22] Filed: Feb. 7, 1974 [21] Appl. No.: 440,398

[52] US. Cl. 110/18 R, 110/72 B, 236/15 C [51] Int. Cl. F23g 7/00 [58] Field of Search 110/7 A, 18 R, 18 C, 72 B;

[56] References Cited UNITED STATES PATENTS 2,283,745 5/1942 Lines 110/72 B 3,323,475 6/1967 Melgaard ll0/18 R 3,710,738 1/1973 Franklin 110/18 R Primary Examiner-Kenneth Sprague Attorney, Agent, or Firm-James D. Givnan, .lr.

[ 5 ABSTRACT A control system responsive to the draft flow of air within a burner for regulating the supply of combustion air to the burner interior. A plate is disposed within a draft opening of the burner with linkage connecting the plate and the underfire air system of the burner. The linkage is operable to translate plate motion into movement of components associated with the underfire system to increase or decrease underfire air in relation to internal burner temperatures as the draft flow of air is proportional to burner temperatures.

7 Claims, 7 Drawing Figures PATENTEL NOV I 9 I974 SHEET 10$ 2 'PATENTEL HUV 191974 SHEH 2 OF 2 I I II I Pu... m W 1 BACKGROUND OF THE INVENTION The present control system is described in conjunction with the underfire ventilating system of a waste wood burner of the type commonly found adjacent wood products mills for the burning of waste. Such burners are commonly termed Wigwam burners by reason of their conical shape.

Considerable effort has been and is being expended to increase the efficiency of wood waste burners, such effort being expended primarily as a result of stringent air quality controls now in effect throughout the United States and certain foreign countries. Such burners serve to dispose of the'more or less continuous flow of waste wood from the adjacent mill which waste is fed by conveyor onto a burning fuel mound.

Temperatures within wood waste burners fluctuate through a wide range with the optimum operativetemperature's being in the range of 700F to 900F (exit gas temperature) with such temperatures indicative of efficient combustion of waste with a minimum of smoke and particulate being released to the atmosphere. Examples of current burner modification to achieve optimum efficiency are found in the following US. Pat. Nos. which generally disclose ventilating means providing both underfire air directed upwardly into the fuel mound and overfire air directed inwardly onto the fuel mound: 3,447,493; 3,472,184; 3,602,161; 3,638,591; 3,669,039; and 3,731,640. Various arrangements are disclosed for controlling the volume of both underfire and overfire air which arrangements most often include costly electro-mechanical components of high original cost, and requiring periodic maintenance or replacement. For example, temperature sensors responsive to burner air adjacent the burner upper end may be combined with various automatic controls which in turn regulate, among other components, the flow of underfire and overfire air. Other components of the burner structure may be controlled by such sensors to achieve the rapid acceleration of burner temperatures to a desired temperature and sustaining the burner temperature thereat until shutdown at the end of a work period.

While satisfactory results have been achieved with certain burner modification work the modification cost for installing thermally controlled equipment is substantial. Equally important, burner control systems incorporating costly and complicated electronic components constitute a maintenance problem in that trouble shooting and repair or replacement of malfunctioning control equipment is not within the capability of a millwright but instead requires the services of a skilled technician. As continued operation of an impaired burner incurs the risk of substantial fines or injunctions by local air quality control agencies the burner must ordinarily be shut down until such time as qualified personnel, and in some instances replacement components, are available. Such renders a severe hardship on mill operations and in some instances results in closure of the mill until such repair work can be accomplished.

' SUMMARY OF THE INVENTION The present invention is embodied within damper structure in communication with the interior of a waste burner with damper actuated linkage controlling the flow of pressurized air to the burner interior. The damper is responsive to draft flow resulting from an air pressure differential within the burner which pressure will normally be below the ambient atmospheric pressure. With exit-gas being discharged from the upper end of the burner, an area of reduced pressure exists within the burner about the fuel mound. The present invention utilizes the barometric differential and the induced draft flow of ambient air to control the flow of pressurized air to the burner interior. In the presence of adverse burner temperatures underfire air may be curtailed with air being admitted to the burner shell for cooling purposes. The draft, proportional to burner temperatures, impinges on a plate which in turn regulates underfire air thus dispensing with the need for costly and complicated electronic components heretofore used for such purposes.

Important objects of the instant control system include the regulation of burner temperatures by a draft responsive damper mechanism linked with means regulating a flow of pressurized air; a control system capable of utilizing mechanical or other linkage mechanisms readily adjustable and serviceable by the mills millwright; a control system permitting dual use of blower air to provide a source of both underfire and overfire air; a control system which in addition to controlling underfire air may divert air from underfire ducting for passage into the burner shell cooling same to avoid structural shell damage from excessive temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. I is a side elevational view of the present control system shown in conjunction with a wood waste burner,

FIG. IA is a fragmentary view of a burner with a modified system, I

FIG. 1B is an enlarged view of valve plate and control arm structure of FIG. 1A,

FIG. 2 is an elevational of the system,

FIG. 3 is a view similar to FIG. 2 showing a modified form of the invention, and

FIG. 4 is a plan view taken downwardly along line 4--4 of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With continuing reference to the drawings wherein applied reference numerals indicate parts similarly identified in the following description, the reference numeral 1 indicates the shell of a burner structure of the type commonly found at wood product mill sites for the burning of waste material. While the present invention is disclosed in association with such a burner it is support of combustion. Different underfire systems are presently in use, such having in common, a source of pressurized air such as a centrifugal blower 5, ducting 6, plenum 7 and air dispersing ducts 8 terminating in upwardly opening vents 9. Grates are also utilized to admit air upwardly into a fuel mound. The underfire structure above described is exemplary only of current underfire ventilating systems as it is understood that various other ductwork configurations are equally compatible with the present invention. The operation of underfire blowers in the prior art systems is controlled, for the most part, by thermocouples and related switching mechanisms.

With attention now to the first described embodiment of the present invention, draft conduits are indicated at 10 in place on and extending through the burner shell I. Said conduits permit a draft flow of air to also support combustion of the waste pile which air may be termed overfire air. Shown within one of said conduits are draft sensing means 11 in the form of a plate. Bearings 12 pivotally receive plate supporting pivot pins 13. The plate is provided with an adjustable weight 14 including a threaded arm 15 extending centrally through the plate. Accordingly, weight 14 may be adjusted toward or away from plate 11 thereby determining the sensitivity of the plate to conduit air flow resulting from differential pressures exteriorly and interiorly of the burner shell.

Indicated at 16 is a rod associated with one of said draft conduits and constituting motion translating means, with one end thereof pivotally attached at 17 to plate 11 while, in a similar manner, the remaining rod end is remotely attached at 18 to a valve plate 20.

Associated with blower 5 and ducting 6 thereof is a housing 22 which defines a plenum 21 charged with blower pressurized air. A conduit segment 23, in communication with plenum 21 constitutes a vent communicating said plenum with the atmosphere. Swingably mounted within said conduit segment is valve plate shown closing said segment or vent when positioned transversely therein. Valve plate 20 is desirably provided with an adjustable weight 24 positionable towards or away from the plate by means of a threaded shaft 25 in threaded engagement with the plate. Indicated at 26 are bearings receiving plate supporting pivot pins 27. Plate 20 is accordingly positionable in response to movement of plate 11 which, in turn, is responsive to an inward draft flow of ambient air.

In operation, blower 5 delivers pressurized air to the underfire system 4 for upward discharge into the fuel mound. Thereafter internal burner temperatures will result in gas exiting through the burner dome 2 resulting in an air pressure differential between the air in the burner interior adjacent the fuel mound and ambient or atmospheric air. Hereinafter for the sake of convenience, a negative pressure (relative to atmospheric) may be said to exist within the burner or at least the lower portion thereof with the pressure differential proportional to internal burner temperatures. This negative pressure induces an inwardly directed draft or flow of air through conduit 10 to the burner .interior. Clockwise movement of plate 11 results in displacement of rod 16 to the left, as viewed in FIG. 2, the displacement being proportional to the flow rate of air through conduit 10. The motion of plate 11 is translated via rod 16 to valve plate 20 to open conduit segment 23 to vent blower pressurized air from plenum 21. Accordingly,

blower output through duct 6 of the underfire system is diminished to reduce the burn rate of the waste pile. Internal burner temperatures will accordingly be reduced by ambient air.

Adjustment of weight 14 on plate 11 will render the plate responsive to a predetermined draft flow through conduit 10. The draft may be calculated as follows:

Where: Dt draft, inches W.C.

P Barometric pressure, PSI

H Height of burner, ft.

T Ambient temperature, R

T Average Stack temperature, R

Plate 11 may be set to open at a pressure differential correlated to a temperature point sensed at the upper portion of the burner shell. Said temperature point is desirably within the 700F 900F range wherein emissions are well below critical amounts. Air entering conduit segments 10 primarily serves to mix with air within the burner to reduce the temperature of same and ultimately cool the inner surface of the burner shell to prevent structure damage to same. Simultaneously, underfire air to the waste pile is diminished to the extent that the burn rate is lessened to contribute to a reduction in burner temperature.

In FIGS. 1A and IE I show a somewhat modified arrangement with similar structure being indicated by prime reference numberals. In communication with housing 22' is a conduit 30 having a discharge end associated with burner shell 1. Air from blower 5 is directed into the burner shell past a valve plate 31 similar to the first described valve plate. In distinction to the first described system, the present system routes air into and along the burner shell interior primarily for the purpose of reducing burner temperatures to maintain same below that level at which damage to the burner would occur. Conduit 30 may be radially disposed of the burner shell or tangential to best suit the cooling task at hand. A linkage rod 32 interconnects a draft sensing plate 11 in draft conduit 10 with valve plate 31 in a manner translating movement of plate 11 as earlier described in the first form of the invention. Valve plate 31 is carried by a pivotal support rod 33 to which is affixed a control arm 34 which in turn is in pivoted attachment at 35 with rod 32.

In FIGS. 3 and 4 another modified form of the invention is disclosed wherein underfire air is again regulated by internal burner temperatures. Double prime reference numerals indicate components similar to those earlier described. A linkage rod 36 is pivotally coupled at its inner end 37 to a draft sensing plate 11" and extends outwardly of conduit segment 10 and thence rearwardly into a pivotal connection at 37 with a door 40 of a blower intake housing 41. Said door is hinged at 42 and normally rests in a closed position to close an air inlet 43 in the housing. Means at 45 may be utilized to counterbalance the door against the influence of the blower intake to permit door control by plate 11" and I rod 36. With plate 11" and door 40 in the position shown the blower may supply the underfire air system via duct 6" with a normal quantity of air to promote efficient burning of the fuel mound.

In an overheat condition of the burner the resulting elevated pressure differential within the lower area of the burner will increase the draft flow within conduit 10" to the extent plate 11" is repositioned clockwise. Motion translating rod 36 is displaced to the left to reposition door 40 towards a closedposition to restrict the entry of ambient air into housing 41 and accordingly to the blower intake at 44. Delivery of blower air into duct 6" of the underfire system is thereby restricted. Upon a lowering of burner temperatures the pressure differential between the burner area adjacent the fuel mound and the ambient pressure is accordingly reducedto lessen the draft through conduit segment 10" permitting plate 11" to return to its initial position 'shown'in FIG. 3. The operating cycle of the invention is affected insignificantly by irregular feed rates of waste material to the burner, with changes occurring only in the durations between opening and closing movement of the draft sensing plate 11 and its counterparts indicated by prime numbers.

While I have shown but a few embodiments of the in-' vention it will be apparent to those skilled in the art that the invention may be embodied still otherwise without departing from the spirit and scope of the invention.

Having thus described the invention, what is desired to be secured under a Letters Patent is:

1. An underfire air control system preventing adverse temperatures within the metal shell of a burner structranslating means interposed between said draft sensing means and said regulating means for translating movement of said draft sensing means into controlled movement of said regulating means whereby upon a pre-determined draft occurring in the burner opening said regulating means will diminish the supply of underfire air to the burner interior with a consequent reduction in internal burner temperatures.

2. The underfire air control system claimed in claim 1 wherein the draft sensing means is a plate pivotally mounted within a length of conduit, said plate including adjustable means for varying the plates responsiveness to drafts within the conduit.

3. The underfire air control system as claimed in claim 2 wherein said interposed means includes mechanical linkage in pivotal attachment with said draft sensing means.

4. The underfire air control system as claimed in claim 3 wherein said regulating means functions to bleed air from the downstream side of the pressure source.

5. The underfire air control system as claimed in claim 4 wherein said regulating means comprises a valve plate, said linkage additionally in pivotal attachment to said valve plate.

6. The underfire air control system as claimed in claim 4 additionally including conduit means communicating the downstream side of the underfire air system with the burner interior, said regulating means additionally' operable to divert air into the last mentioned conduit means for delivery of pressurized air to the burner interior to reduce burner temperatures.

7. The underfire air control system as claimed in claim 3 wherein said regulating means functions to restrict the entry of air into the upstream side of the pres- 

1. An underfire air control system preventing adverse temperatures within the metal shell of a burner structure, said burner structure including an underfire system for delivery of combustion supporting air from a pressure source to the base of piled waste material, said control system comprising, draft sensing meAns disposed within a draft opening in the burner structure in communication with the atmosphere and the burner interior, said draft sensing means positionable in response to a draft within said opening, regulating means associated with the underfire system and regulating the volume of air delivered from the pressure source to the burner interior, and translating means interposed between said draft sensing means and said regulating means for translating movement of said draft sensing means into controlled movement of said regulating means whereby upon a pre-determined draft occurring in the burner opening said regulating means will diminish the supply of underfire air to the burner interior with a consequent reduction in internal burner temperatures.
 2. The underfire air control system claimed in claim 1 wherein the draft sensing means is a plate pivotally mounted within a length of conduit, said plate including adjustable means for varying the plates responsiveness to drafts within the conduit.
 3. The underfire air control system as claimed in claim 2 wherein said interposed means includes mechanical linkage in pivotal attachment with said draft sensing means.
 4. The underfire air control system as claimed in claim 3 wherein said regulating means functions to bleed air from the downstream side of the pressure source.
 5. The underfire air control system as claimed in claim 4 wherein said regulating means comprises a valve plate, said linkage additionally in pivotal attachment to said valve plate.
 6. The underfire air control system as claimed in claim 4 additionally including conduit means communicating the downstream side of the underfire air system with the burner interior, said regulating means additionally operable to divert air into the last mentioned conduit means for delivery of pressurized air to the burner interior to reduce burner temperatures.
 7. The underfire air control system as claimed in claim 3 wherein said regulating means functions to restrict the entry of air into the upstream side of the pressure source. 